The details and benefits of non-pneumatic tire constructions are described e.g., in U.S. Pat. Nos. 6,769,465; 6,994,134; 7,013,939; and 7,201,194. Certain non-pneumatic tire constructions propose incorporating a shear band, embodiments of which have also been described in e.g., U.S. Pat. No. 7,201,194, which is incorporated herein by reference. Such non-pneumatic tires provide advantages in tire performance without relying upon a gas inflation pressure for support of the loads applied to the tire.
An example of a tire 100 having a ring-shaped shear band 110 is shown in FIG. 1. Tire 100 also includes a plurality of tension transmitting elements, illustrated as web spokes 150, extending transversely across and inward from shear band 110. A mounting band 160 is disposed at the radially inner end of the web spokes. The mounting band 160 anchors the tire 100 to a hub 10. A tread portion 105 is formed at the outer periphery of the shear band 110 and may include e.g., grooves or ribs thereon.
Referring to FIG. 2, which shows the tire 100 in section view in the meridian plane (but without tread portion 105), the reinforced shear band 110 comprises a shear layer 120, an innermost reinforcement layer 130 adhered to the radially innermost extent of the shear layer 120, and an outermost reinforcement layer 140 adhered to the radially outermost extent of the shear layer 120. The reinforcement layers 130 and 140 have a tensile stiffness that is greater than the shear stiffness of the shear layer 120 so that the shear band 110 undergoes shear deformation under vertical load.
More specifically, as set forth in U.S. Pat. No. 7,201,194, when the ratio of the elastic modulus of the reinforcement layer to the shear modulus of the shear layer (E′membrane/G), as expressed in U.S. Pat No. 7,201,194, is relatively low, deformation of shear band 110 under load approximates that of a homogenous band and produces a non-uniform ground contact pressure. Alternatively, when this ratio is sufficiently high, deformation of the shear band 110 under load is essentially by shear deformation of the shear layer with little longitudinal extension or compression of the reinforcement layers 130 and 140. As indicated in FIG. 1, a load L placed on the tire axis of rotation X is transmitted by tension in the web spokes 150 to the annular band 110. The annular shear band 110 acts in a manner similar to an arch and provides circumferential compression stiffness and a longitudinal bending stiffness in the tire equatorial plane sufficiently high to act as a load-supporting member. Under load, shear band 110 deforms in contact area C with the ground surface through a mechanism including shear deformation of the shear band 110. The ability to deform with shear provides a compliant ground contact area C that acts similar to that of a pneumatic tire, with similar advantageous results.
The shear layer 120 may be constructed e.g., from a layer of material having a shear modulus of about 3 MPa to about 20 MPa. Materials believed to be suitable for use in the shear layer 120 include natural and synthetic rubbers, polyurethanes, foamed rubbers and polyurethanes, segmented copolyesters, and block co-polymers of nylon. The first 130 and second 140 reinforcement layers comprise essentially inextensible cord reinforcements embedded in an elastomeric coating. For a tire constructed of elastomeric materials, reinforcement layers 130 and 140 are adhered to the shear layer 120 by the cured elastomeric materials.
As stated above, a shear band such as band 110 provides a longitudinal bending stiffness during operation of the tire 100. For certain applications, it is desirable to maintain the overall thickness—along the radial direction R—of shear band 110 while simultaneously increasing its bending stiffness. For example, a designer may seek to maintain the overall diameter of non-pneumatic tire 100 and the shear beam thickness while increasing the bending stiffness of the shear band 110 in order to change the performance characteristics of tire 100. Conversely, for certain other applications, it is desirable to decrease the thickness of shear band 110 while maintaining the bending stiffness of tire 100 and thus reduce mass.
Accordingly, a method for the design of such shear bands and shear bands constructed from such method would be particularly useful. More particularly, a method that allows the designer of a non-pneumatic tire to improve certain mechanical properties of a reference shear band such as e.g., bending stiffness while maintaining the overall dimensions of the non-pneumatic tire would be particularly useful. A method that also allows a designer to decrease the radial thickness of a shear band while maintaining or improving upon certain mechanical properties would also be useful. These and other advantageous aspects of the present invention will be apparent from the description that follows.